Air-dried polyester coating and application

ABSTRACT

An air-dried polyester coating which is adapted to be applied in successive layers with a very short time interval between applications and which cures to a sandable hardness very rapidly. The polyester is an air-drying resin, and it is cross-linked with bromo- or chlorostyrene monomer.

O Umted States Patent [151 3,647,516

Edwards 1 Mar. 7, 1972 [54] AIR-DRIED POLYESTER COATING 3,029,159 4/1962Bliven et al. ..117/148 X AND APPLICATION 3,240,619 3/1966Winchester.... ..117/148 X 3,275,710 9/1966 Wooster ...1 17/148 XInventor: Kenneth Edwards, 1130 Rossmoyne 3,498,828 3 1970 Small ..117/161 UC x Ave., Glendale, Calif. 91207 Filed: Oct. 1969 OTHERPUBLlCATlONS Polyester by Edward H. Meyer, Modern Plastic En- [211 PP869,873 cyclopedia, 1965 Ed.,pp. 235- 240.

Primary ExaminerWilliam D. Martin [52] US. Cl ..l17/64, 117/132 B,117/148, Assistant Examiner wmiam R Trenor 1 17/161 7/161 UCAttorney-Beehler & Arant [51] Int. Cl. ..B44d l/26,C09d 3/68 Anair-dried polyester coating which is adapted to be applied [56] m-aCited in successive layers with a very short time interval betweenapplications and which cures to a sandable hardness very UNITED STATESPATENTS rapidly. The polyester is an air-drying resin, and it iscrosslinked with bromoor chlorostyrene monomer. 2,537,018 l/l951 Barrett..1 17/148 X 2,967,174 1/1961 Bartl ..l17/148 X 9 Claims, No DrawingsAIR-DRIED POLYESTER COATING AND APPLICATION This invention relates topolyester coatings and the application of polyester coatings to varioussubstrates. More particularly, this invention relates to the applicationof unsaturated air-drying polyester coatings to various substrates andthe resultant coatings, wherein the unsaturated polyester is crosslinkedwith chloroor bromostyrene.

Previously, air-drying polyester coatings suffered from severaldisadvantages which have been overcome according to the presentinvention.

According to the present invention, it is possible to apply a coating ofunsaturated air-drying polyester resin containing chloroor bromostyreneand obtain a tack free surface with a very short period of time. Thepolyester coating cures completely within a short period of time. Thisrapid curing rate permits the application of plural coats one uponanother at frequent time intervals and also permits the final finishingof the polyester coatings by sanding, polishing, buffing, or otherwisemechanically abrading the surface where these surface treatingprocedures are to be employed.

The resultant coating is a very dense film which is highly resistant tomoisture penetration and is relatively strain free. The coating shrinksas it cures until it reaches a particular thickness within a few hoursafter it is applied and does not shrink further even over extendedperiods of time. This is very important where the coating is applied toa substrate, such as wood, where the grain produces slightirregularities in the surface of the substrate which appear on thesurface of the coating if the coating shrinks too much.

A wide variety of unsaturated air-drying polyester resins are disclosedin the prior art. The resins which are particularly applicable to thisinvention include only those in which the airdrying properties areinherent in the polyester itself, and does not include those whereadditional physical means, such as wax or physical shielding, areemployed to protect the surface of the polyester from exposure to oxygenwhile it is cured.

The air-drying or nonair-inhibited unsaturated polyesters suitable foruse in this invention are those which can be cured as thin films in thepresence of air or oxygen to produce fully cured surfaces. in general,the polyesters, which are suitable for use in coating compositions, areunsaturated polyesters which have been modified to prevent airinhibition. In general, the modifications of the unsaturated polyesterstake the form of modification to the acid or glycol components, or theaddition of copolymerizable materials to the unsaturated polyesters.

Nonair-inhibited polyester coatings have been produced using isophthalicor tetrahydrophthalic anhydride or acid in admixture with anethylenically unsaturated dicarboxylic acid of two to 18 carbons whichis free of nonbenzenoid unsaturation where the isophthalic ortetrahydrophthalic anhydride or acid is present in an amount at leastequal to mol percent of the total dicarboxylic acid content in theresin. Ethylenically unsaturated dicarboxylic acids, which are suitablefor admixture with the isophthalic or tetrahydrophthalic anhydride oracid include; for example, maleic, fumaric, chloromaleic, itaconic,citraconic, and mesaconic, acids, and anhydrides where they exist, andthe like. Suitable dihydric alcohols and glycols for use withisophthalic or tetrahydrophthalic anhydride or acid containingpolyesters include; for example, ethylene glycol, propylene, butylene,diethylene, dipropylene, triethylene, and higher glycols, 1,2-propyleneglycol, 1,3- dipropane diol, thiodiglycol, halogen substituted glycols,and the like. These are conventional glycols known in the art to beuseful in the preparation of polyesters.

The glycol component of the polyester can be modified to produce thedesired air-drying films. All or a part of the conventional diols can bereplaced with ether-oxygen containing alcohols; such as, thepolyalkylene ether glycols, polyethylene ether glycol, and polypropyleneglycol. Also, air-cured films which are hard and tough and exhibitoutstanding gloss characteristics may be produced by using aromaticether glycols and ethylenically unsaturated aliphatic ether glycols;such as, for example, glycerol alpha-ally] ether and trimethylol propanediallyl ether, the reaction products of ethylene and propylene oxideswith trietylene-. tetraethylene-, pentaethylene-, hexaethylene-, andpentabutylene glycols, glycerol monoallyl ether, and the like. The etherglycols are preferably used in admixture with conventional polyesterforming glycols, such as propylene and ethylene glycol for use in thepreparation of a polyester. Preferably at least 30 mol percent of theconventional glycol is replaced by the ether glycol. Conventionaldicarboxylic acids are used-with the admixtures of ether glycols andglycols to produce polyesters. Such dicarboxylic acids include, forexample, maleic and fumaric acids, anhydrides, and the like.

A wide variety of air-drying polyesters and their methods of preparationare described in Unsaturated Polyesters: Structure and Properties,Herman V. Boenig (1964), Elsevier Publishing Company, New York, at pagesI88 through 204. The disclosure of nonair-inhibited polyesters and theirpreparative methods are incorporated herein by reference.

The cross-linking monomer which is employed according to the presentinvention is either a monochloroor a monobromostyrene. The particularisomer employed is not critical; however, in practice a mixture ofortho-, meta-, and paraisomers are used.

The polyester resins suitable for this invention are ordinarily preparedby condensing one or more organic acids with one or more polyhydricalcohols, one or bothof the acids or alcohols contains an ethylenicunsaturation. The resultant polyester resin is dissolved in amonobromoor monochlorocross-linking agent. The polyester polymerizablemonomer compositions, which are substantially l00 percent polymerizable,are conventionally stabilized with inhibitors, such as, for example,hydroquinone to pennit their being stored for extended periods. Thepolyester resins can be utilized in the clear, unpigmented state, or ifdesired, it may be admized with fillers, dyes, pigments, opacifiers,lubricants, plasticizers, other modifying agents, and the like.

The substrate to which the coatings of this invention are adhered asfilms or impregnates include wood, metal, ceramics, cloth, interwovenfibrous material, concrete, and the like.

The following examples illustrate the best modes presently known to mefor practicing the principles of this invention.

EXAMPLE 1 An air-drying unsaturated polyester is prepared from thefollowing ingredients:

Grams Diethylene glycol 445 Maleic anhydride 2l0 Phthalic acid 345 Theingredients are cooked in an inert nitrogen atmosphere until thetemperature of the mass reaches Centigrade whereat an exothermicreaction starts. The temperature of the mass is allowed to rise to 200C. and is held at that temperature until an acid number of about 50 isreached. One-hundred grams of trimethylol propane diallyl ether is thenadded. A quantity of hydroquinone in the amount of 0.008 weight percentis added, and the admixture is cooled to a temperature of C. Theadmixture is divided into three equal parts and each part is mixed withan equal weight of one of styrene monomer, monochlorostyrene monomer,and monobromostyrene monomer.

The three admixtures are then allowed to cool.

EXAMPLE II The unsaturated polyester-monochlorostyrene admixtureprepared in Example I is admixed with 1 weight percent of methylethylketone peroxide and is sprayed on a clean sanded poplar wood surface atan ambient temperature of about 70 F. The sprayed surface is allowed tostand for 24 minutes and is then sprayed with the same composition asecond time. This procedure is repeated a third time 24 minutes afterthe second application. The surface is tack free 24 minutes after theapplication of each coat. The resultant polyester coated poplar woodspecimen is allowed to stand undisturbed for 2 hours at which time it issanded and buffed with ease to a very high gloss finish. The .coatinghas a very pleasing appearance of great depth. The unsanded thickness ofthe coating 2 hours after the application of the last polyester coatingis one-sixteenth of an inch. The sanding and polishing operation removesapproximately one sixty-fourth inch from the polyester coating. Thecoating is examined after six months and is found to be unchanged in anydetectable feature. The surface of the coating shows no tendency tofollow the grain pattern of the underlying poplar wood.

EXAMPLE Ill The unsaturated polyester-monobromostyrene admixtureprepared in Example I is admixed with 1 weight percent of methylethylketone peroxide and is sprayed on a clean sanded poplar wood surface atan ambient temperature of about 70 F. The sprayed surface is allowed tostand for 30 minutes and is then sprayed with the same composition asecond time. This procedure is repeated a third time 30 minutes afterthe second application. The resultant polyester coated poplar woodspecimen is allowed to stand undisturbed for 2% hours at which time itis sanded and buffed with ease to a very highgloss finish. The coatinghas a very pleasing appearance of great depth. The unsanded thickness ofthe coating 2% hours after the application of the last polyester coatingis one-sixteenth of an inch. The sanding and polishing operation removesapproximately one sixty-fourth inch from the polyester coating. Thecoating is examined after 6 months and is found to be unchanged in anydetectable feature. The surface of the coating shows no tendency tofollow the grain pattern of the underlying poplar wood.

EXAMPLE IV The unsaturated polyester-styrene admixture prepared inExample I is admixed with 1 weight percent of methylethyl ketoneperoxide and is sprayed on a clean sanded poplar at an ambienttemperature of about 70 F. The sprayed surface is allowed to stand for45 minutes and is then sprayed with the same composition a second time.This procedure is repeated a third time 45 minutes after the secondapplication. The resultant polyester coated poplar wood specimen isallowed to stand undisturbed for 4% hours at which time it is sanded andbuffed to a very high-gloss finish. The sanding and buffing takes longerthan with the halostyrene systems, and the appearance of the finalproduct is not as pleasing. The unsanded thickness of the coating 4%hours after the application of the last polyester coating isone-sixteenth of an inch. The sanding and polishing operation removesapproximately one sixtyfourth inch from the polyester coating. Thecoating is examined after 6 months and is found to have shrunk anotherone sixty-fourth inch. The surface of the coating shows some tendency tofollow the grain pattern of the underlying poplar wood.

EXAMPLE V The examples may be repeated using an equimolar mixture ofisophthalic and maleic anhydrides or a mixture of tetrahydrophthalicanhydride and fumaric acid in the molar ratio of l to 3, in place of themaleic anhydride-phthalic acid mixture; polyethylene ether glycol inplace of the diethylene glycol; and the replacement of 80 weight percentof the diethylene glycol with glycerol monoallyl ether. In each instancethe formulations, wherein chlorostyrene or bromostyrene is used, willcure faster and produce a harder, denser, more adherent coating withmore uniform properties under a wider variety of environmentalconditions of temperature and humidity than will be produced with thestyrene con- 1 taining formulations.

The coatings in this invention may be applied using dual chambermetering spray guns in which the peroxide catalyst is admixed with thepolyester resin at the time the polyester is sprayed onto the surface ofthe substrate. if desired, a curtaining application may be employedwhere the catalyst and polyester are admixed in a chamber which opensinto a downwardly presented slot. The slot is of accurate, predetermineddimensions so that a thin film of polyester flows continuouslydownwardly through the slot. The object to be coated is then passedunderneath the slot through the curtain of falling polyester resin. Theobject is passed through the curtain of resin at such a rate that itssurface receives a uniform application of polyester resin as it passesthrough the curtain.

Where slow catalyst systems are used, it is possible to employconventional spraying equipment having only one chamber; however, thecuring times are so long as to be impractical for most commercialoperations. Various catalyst systems for unsaturated air-dryingpolyesters are known in the art. The selection of an appropriate knowncatalyst system for the desired rate of cure is within the skill of theart; however,

the use of a monohalostyrene instead of styrene will markedly increasethe rate of cure and will improve the density and other properties ofthe final cured coating.

The bromoand chlorostyrene containing unsaturated airdrying polyesterresins may be applied to the desired substrate in. a wide variety ofthicknesses ranging from as little as about 0.1 mils or less toone-quarter inch or more. The thicker coatings are generally built upthrough the successive application of a plurality of thin coatings. Withhalostyrene containing polyesters it generally requires fewer coats tobuild up the desired thickness than is required when styrene is used asthe cross-linking monomer.

One particularly desirable application for the coatings of thisinvention is on high quality wooden furniture and musical instrumentswhere a deep, clear finish is necessary for aesthetic purposes. Thepreferred formulation for use on wooden surfaces is that where thechlorostyrene containing resin of Example I is employed except thatpropylene glycol is used instead of diethylene glycol. The coating isvery dense, hard and resistant to cigarette burns, hot dishes, and othercommon household sources of fire damage to wood finishes. This fireresistance is obtained without the addition of any additive which mighttend to cloud the coating and thus detract from the beauty of the woodfinish. This finish has a very clear, deep and aesthetically pleasingappearance.

The polyester coatings according to this invention are very dense andresistant to moisture penetration. This dense, impenetrable coatingstabilizes the wood and prevents its deterioration. The dense, hardsurface is very amenable to sanding and polishing.

The application of a polyester coating of this invention to an aluminumsubstrate results in a coating which is very tightly adhered to thealuminum surface and does not tend to peel or flake. The preferredpolyesters for application to aluminum or other metallic surface is thatwhere the diol is relatively longchained so as to impart flexibility tothe resultant coating. This permits it to flex with the metallicsubstrate without cracking.

The monochlorostyrenes are preferred for use in the coatings of thisinvention for practical reasons. The monochlorostyrenes are more readilyavailable, and their properties are more thoroughly known than are thoseof the monobromostyrenes.

The chloroand bromostyrenes are less volatile than styrene so that lessof the halostyrenes are lost from the coating while it is being cured.This results in a coating which has more uniform properties throughoutits thickness. Also, the temperature and humidity conditions under whichspraying takes place are not so critical with halostyrenes because oftheir reduced volatility. With styrene containing polyester coatings,the properties often vary within rather wide limits because of thedifferent temperatures and humidities prevailing during differentseasons or even during difi'erent hours of the same day. Also, thedecreased quantity of volatile material in the air at the work sitereduces the hazards to health occasioned by breathing organic vapors origniting an explosive atmosphere.

The halostyrene monomer is employed in admixture with the air-dryingunsaturated polyester in an amount ranging from about to 80 weightpercent of the polyesterhalostyrene admixture, and preferably from about30 to 70 weight percent with many admixtures being between about 40 and50 weight percent.

The rate of cure is dependent to a certain extent upon the temperatureat which the cure is carried out. Satisfactory cures may be obtainedusing the unsaturated air-drying polyester-halostyrene admixtures ofthis invention at temperatures of from about 60 Fahrenheit to 350Fahrenheit. The higher temperatures are produced by stoving, generallywith infrared heat lamps. When the substrate to be coated by thepolyester-monohalostyrene admixture is a wood work piece, the cure isgenerally carried out at the ambient temperature of from about 60 F. to100 F. Under these conditions, it generally takes from about 20 to 30minutes for the coating to reach a tack free state, and about 2 hoursfor it to reach a degree of hardness where it can be mechanicallyabraded, such as, for example, by sanding or buffing. Where metallicsubstrates are employed and it is desired to greatly increase the curingrate, stoving at temperatures of up to 325 F. and even up to 350 F. willreduce the curing time to between about 10 and 15 minutes for a finishwhich is hard enough to mechanically abrade.

When desired a cobalt compound may be employed to cause the drying ofthe surface. The cobalt also brings about the-decomposition of theperoxide catalyst. Care should be taken not to mix the cobaltaccelerator and the organic peroxide in the undiluted state.

Where a particularly thin coating, such as, for example, a coating whichis less than 5 or 10 mils thick is desired, it is possible to thin theunsaturated air-drying polyesterhalostyrene compositions with a solvent,such as, for example, ethyl acetate, spray them on to the desiredsubstrate and allow the ethyl acetate solvent to flash off.

If desired, the halostyrene may be diluted with up to as much as 75weight percent of the combined weight of the resultant admixture withstyrene. The benefits of this invention are obtained to a lesser degreewith these styrene diluted chloroand bromostyrene admixtures; however,the preferred admixtures are those in which the halostyrene constitutesat least 50 weight percent and preferably 75 weight percent of the totalstyrene admixture. Admixtures of chloroand bromostyrene may be employedif desired.

When it is desired to employ various pigments, leveling agents, fillersand the like, it has been found that the halostyrene coatings cure muchmore rapidly into a much harder and denser state than do thecorresponding styrene containing polyesters. The greater the loading ofthe polystyrene vehicle with dyes, pigments and the like, the moremarked is the difference between the curing rates of halostyrenecontaining polyesters and styrene containing polyesters. The styrenecontaining polyesters reach a state where they will not cure to a hardsurface at a much lower loading rate than do the halostyrene containingpolyesters.

This difference between the styrene and halostyrene containing vehiclesis particularly marked where the agent with which the vehicle is to beloaded has an inhibiting effect on the curing of the resin. Coppercontaining blue pigments and cadmium red pigments do retard or delay thecuring of polyester resins. The impact of these pigments on the curingrate of halostyrene containing vehicles is substantially less than it ison the curing rate of styrene containing vehicles. Other conventionalcompounding agents also have some retarding or inhibiting effect on thecure of the vehicle when used at highloading rates. The compoundingagents; such as, fillers, colorants, and leveling agents, may beemployed in quantities ranging from less than 1 percent up to 20 or 30or more weight percent of the total weight of the vehicle. Often wherethe substrate is valuable because of its a pearance, such as fine woodenartlcles, the only compoun mg agents employed are inhibitors andcatalysts which are present in amounts of less than 0.1 weight percentof the resin vehicle.

As will be understood by those skilled in the art, what has beendescribed are preferred embodiments in which modifications and changesmay be made without departing from the spirit and scope of theaccompanying claims.

What is claimed is:

l. A method of coating which comprises: admixing an inherentlyair-drying unsaturated polyester with from about 20 to percent by weightof the resultant admixture of a monohalostyrene monomer having a halogenatom with an atomic weight of less than 80 and greater than 34, admixingsaid admixture with a polymerization initiator, applying the initiatedadmixture to the surface of a solid substrate as a film having a curedthickness of from about 0.1 mil to one-fourth inch, and allowing theapplied film to cure in air at a temperature of from about 60 F. to 350F.

2. A method of claim 1 wherein the applied film is allowed to cure at atemperature of less than about F. and a second initiated admixture isapplied to the surface of the first film within about 30 minutes afterthe first film is applied to the solid substrate.

3. A method of claim 1 wherein the applied film is allowed to cure at atemperature of less than about 100 F. and the surface of the appliedfilm is mechanically abraded about 2 hours after the point in time whenthe film was applied.

4. A method of claim 1 wherein the monohalostyrene is monochlorostyreneand the substrate is wood.

5. An article comprising a cured in situ abradable, dense polyestercoating adhered to a substrate, said coating comprising an inherentlynonair-inhibited unsaturated polyester crosslinked with amonohalostyrene, the halogen in said monohalostyrene having an atomicweight below 80 and about 34, said coating having a thickness of fromabout 0.l mil to one-fourth inch.

6. A coating of claim 5 wherein said monohalostyrene ismonochlorostyrene.

7. A coating of claim 5 wherein said monohalostyrene ismonobromostyrene.

8. A coating of claim 5 wherein said substrate is wood.

9. A coating of claim 5 including a coloring agent.

2. A method of claim 1 wherein the applied film is allowed to cure at atemperature of less than about 100* F. and a second initiated admixtureis applied to the surface of the first film within about 30 minutesafter the first film is applied to the solid substrate.
 3. A method ofclaim 1 wherein the applied film is allowed to cure at a temperature ofless than about 100* F. and the surface of the applied film ismechanically abraded about 2 hours after the point in time when the filmwas applied.
 4. A method of claim 1 wherein the monohalostyrene ismonochlorostyrene and the substrate is wood.
 5. An article comprising acured in situ abradable, dense polyester coating adhered to a substrate,said coating comprising an inherently nonair-inhibited unsaturatedpolyester cross-linked with a monohalostyrene, the halogen in saidmonohalostyrene having an atomic weight below 80 and about 34, saidcoating having a thickness of from about 0.1 mil to one-fourth inch. 6.A coating of claim 5 wherein said monohalostyrene is monochlorostyrene.7. A coating of claim 5 wherein said monohalostyrene ismonobromostyrene.
 8. A coating of claim 5 wherein said substrate iswood.
 9. A coating of claim 5 including a coloring agent.